Manufacturers and surface treaters from a variety of industries and professions have long recognized ultrasonic cleaning as an effective means of removing contaminants from a wide variety of substrates. The process has been embraced for multiple industrial, medical, commercial and residential applications as providing excellent penetration of diminutive interstices on intricate devices. In fact, the use of ultrasonic cleaners has become increasingly popular due to government restrictions on the use of chlorofluorocarbons (i.e., 1,1,1-trichloroethane), encouraging many manufacturers to replace conventional solvent-based cleaning methods with equally effective immersion cleaning technologies.
The effectiveness of ultrasonic cleaning relies upon energy released from the creation and collapse of microscopic cavitation bubbles that break up and release contaminants from the surface to be cleaned. A conventional ultrasonic cleaning system includes a radiating diaphragm having at least one ultrasonic transducer (typically piezoelectric or magnetostrictive) mounted thereto, an electrical generator and a tank filled with an aqueous solution. The generator converts a standard electrical frequency of 60 Hz into high ultrasonic frequencies (generally from about 20 kHz to about 80 kHz), causing the transducer to vibrate. Consequent vibration of the diaphragm induces alternating positive and negative pressure waves in the solution to produce micron-size bubbles (this process is known as cavitation). Upon contact with an item to be cleaned, the bubbles implode, releasing jets thereby that travel at speeds of up to 400 km/hr toward the item surface. With the combination of pressure, temperature, and velocity, the jets dislodge contaminants from their bonds with the item surface very effectively (see Jeff Hancock, “Ultrasonic Cleaning”, www.bluewaveinc.com (citing ASM Handbook, Volume 5: Surface Engineering)).
The efficiency of ultrasonic cleaning devices has inured specifically to the benefit of medical, surgical, dental and laboratory applications (collectively “medical” applications). Environmental regulations and health agency guidelines (promulgated by government agencies such as the Occupational Health and Safety Administration and the Centers for Disease Control in the United States and commensurate international agencies) dictate that medical instruments must be maintained with sufficient hygienic standards so as to pre-empt transmission of infection. Due to the danger of hand scrubbing medical instruments, medical offices typically have at least one ultrasonic cleaner in which cleaning, rinsing and drying operations are executed onsite (in some cleaners the option of pre-soaking is also available). An example of such a device is disclosed by U.S. Pat. No. 3,640,295 to Peterson (“Peterson”), which discloses an ultrasonic cleaner in which instruments to be cleaned are moved with respect to a plurality of ultrasonic transducers. The disclosed cleaner includes a tank that houses a circulating fluid means therein and supports multiple transducers thereon. The tank supports a cradle that oscillates with respect to an oscillating frame, wherein the frame moves in a semicircular path within an aqueous solution retained by the tank. A case carrying at least one medical instrument is provided with hingedly attached top and bottom portions and walls having perforations therethrough to accommodate ultrasonic waves. The case is removably mounted in a fixed position with respect to the frame and oscillatable therewith so as to minimize the effects of null points of the ultrasonic waves in the solution.
An alternative to the Peterson device is provided in commercially available table-top ultrasonic cleaners, such as those produced by ESMA. In one model, an ultrasonic cleaner utilizes three tanks in a single housing to effect a complete cleaning, rinsing and drying operation. In this commercial configuration, one tank retains an ultrasonic cleaning solution, an adjacent tank retains an ultrasonic rinsing agent and a third tank applies warm air to effect sufficient drying of rinsed instruments placed therein. The cleaning operation is therefore executed without expensive automated systems, making the device desirable to operate within available space constraints. The need to transfer medical instruments among the tanks (either manually or automatically), however, substantially elevates the risk of cross-contamination due to re-use of solutions or inattention to identification of instruments. Such transfer is eliminated in certain automated ultrasonic cleaners such as those produced by ESMA in the company's E291 and E789 models. Even in these improved models, a hot air drying means is disposed in a tank cover, thereby creating a heavy device that consumes valuable space in a laboratory or medical environment and inhibits use due to the enhanced effort required to lift the tank cover for proper cleaner operation.
In an effort to eliminate the need to manually or automatically transfer parts during an ultrasonic cleaning operation, U.S. Pat. No. 6,102,056 to Kotsopey (“Kotsopey”, the disclosure of which is incorporated by reference herein) discloses an ultrasonic cleaner having a tank with an open top for inserting articles therein. The tank has each of a liquid inlet opening, a liquid outlet opening, an air inlet window and an air outlet duct. A first overflow passage is disposed adjacent the air inlet opening to prevent flow of liquid therethrough. Similarly, a second overflow passage adjacent the air outlet duct prevents liquid from flowing therethrough. In this configuration, a complete cleaning operation (i.e., cleaning, rinsing and drying steps) is performed in a single continuous operation in a manner such that the solution in the tank never interferes with the flow of air therethrough. Although the cleaner disclosed by Kotsopey effectively integrates cleaning, rinsing and drying functions in an automated operation, the cleaner integrates additional structure such as overflow weirs and perforated air distribution channels that provide a heavy, cumbersome structure that is expensive to manufacture and maintain.
Although the aforementioned cleaners sufficiently sanitize medical instruments from immersion processes executed therein, such devices are cumbersome for laboratory and medical applications. The tank constructions of such devices require extra structure that contributes to tank weight and maintenance. For instance, a separate compartment that is required for drying the instruments contributes to manufacturing and maintenance costs and deleteriously exposes electrical components to excess solution. In medical and laboratory environments, such conditions are detrimental to consideration of space constraints and further inhibit proper use of such cleaning devices, thereby contributing to cross contamination risks.
It is therefore desirable to provide an ultrasonic cleaning device that eliminates the disadvantages of conventional immersion cleaners and advantageously consumes minimal space in the user's environment. The entire ultrasonic cleaning operation (i.e., cleaning, rinsing and drying and an optional pre-soaking mode) desirably occurs in a single tank in which the items to be cleaned remain stationary. Instead, the required solutions are poured into and drained from the tank using a trigger function that eliminates complicated tank structure. Hot air is subsequently circulated in the same tank to effect the drying function. Such a configuration not only saves space, but also reduces fiscal and temporal expenditures and cross-contamination risks while advocating an automated process without the need for expensive robotics.